Flotation processes of this type, in which solid impurities are removed by flotation, are known. These include those processes which are used for removing printer's ink from the paper pulp produced from newspaper waste. In these processed air is injected into a suspension of the paper pulp, which is then passed into the lower part of a flotation container. The air can be admixed therewith in a separate mixing chamber, such as that of the type disclosed in SE-PS No. 7704203-4. Prior to being fed into the flotation container, the suspension is passed through the mixing chamber in the form of a thin layer, and at the same time the air is injected into this layer in a transverse direction. It has been found to be difficult, however, to obtain a uniform distribution of the bubbles, especially in connection with high flow rates of the suspension. This applies, for example, in those cases where the suspension is to be fed tangentially into a cylindrical flotation container at a sufficiently high rate so that the suspension is caused to rotate within the container. The purpose of obtaining such rotation of the suspension is to facilitate removal of a foam which is rich in impurities from the surface of the suspension in the container.
It is therefore an object of the present invention to provide a new design for the mixing chambers in such processes so that these aforesaid disadvantages can now be eliminated.